For purposes of varying the operational range of electric meters such as voltmeters, automatic voltage recorders, and the like, it is known to use a device wherein the ends of a potentiometer are connected between the input terminals of the voltage to be observed and a meter is connected by switching to a voltage dividing end having a selected voltage dividing ratio or the voltage dividing ratio is continuously varied by means of a slider and is set at a selected value with a vernier scale or the like. However, these arrangements are subject to defects in that, in the first case, if the number of range switching levels or steps is too high, a great many values of resistances will be required and will be difficult to manufacture and, in the second case, an accurate setting is difficult and corrective measures are required.